Aniline was found to polymerize slowly and spontaneously on the platinum and palladium metal surfaces in an aqueous acid solution of the monomer. The phenomenon was thus equivalent to an "electroless polymerization" process. The polyaniline (PANI) so-deposited were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The chemical state of the electroless deposited PANI film was near to that of the 75% intrinsically oxidized nigraniline (NA) state of PANI. The electrolessly deposited PANI films exhibited similar protonation-deprotonation behavior as that of the aniline homopolymer. The amount of the PANI deposited on the metal surface was affected by the monomer concentration, the nature of the acid medium, and the oxygen content in the reaction medium. (C) 2002 Elsevier Science B.V. All rights reserved.